Harlequin Rasbora (Red Rasbora) Fish Species Profile

Characteristics, Origin, and Helpful Information for Hobbyists

Harlequin rasbora fish with yellow and black scales swimming closeup

The Spruce / Adrienne Legault

Fish hobbyists love the harlequin rasbora—it has a beautiful metallic color and it is easy to care for. A large school makes an aquarium vivid and vibrant with movement. This is a great fish for a smaller-sized community tank as it is peaceable with most other species. It is a smaller fish, so keep it with like-sized specimens; larger fish might be attracted by its shimmer and try to make a meal out of it.

Species Overview

Common Name: Red rasbora

Scientific Name: Trigonostigma heteromorpha

Adult Size: 1.75 inches (4.5 centimeters)

Life Expectancy: 6 years


Family Cyprinidae
Origin Southeast Asia, Malaysia, Singapore, Sumatra, Thailand
Social Peaceful, suitable for community tank
Tank Level Top to mid-dwelling
Minimum Tank Size 10 gallon
Diet Omnivore
Breeding Egglayer
Care Intermediate
pH 6.0 to 7.5
Hardness Up to 12 dGH
Temperature 73 to 82 F (23 to 28 C)
Harlequin rasbora fish with orange and black scales swimming

The Spruce /Stefan Maurer

Origin and Distribution

The harlequin rasbora is a native of Malaysia, Singapore, Sumatra, and southern Thailand. It inhabits streams and waters that are characterized principally by their low mineral content and high concentrations of dissolved humic acids, which is typical of water that flows through swamped forests. The waterlogged soils of these forests inhibit the complete decay of leaf litter, resulting in the formation of peat, which leaches humic acids. These conditions resemble those found in the blackwater habitats of South America.

Colors and Markings

Of the more than five dozen species of rasbora, the harlequin is arguably the most popular of them all. Often referred to as a red rasbora, the body is a reddish-copper color that is accented by a striking black wedge covering the rear half of the body. The distinguishing triangular patch begins near the dorsal fin and comes to a point near the base of the caudal fin.

This species looks similar to the Pork Chop or Lamb Chop Rasbora (T. espei). and the Narrow Wedge Rasbora (T. hengeli), and Somphong's Rasbora (T. somphongsi), and these fish species can be differentiated primarily by the size of the dark "wedge." These species of rasboras are listed from largest to smallest triangular patch.


The harlequin rasbora is a shoaling fish; it should be kept in schools of eight to 10 individuals. Schools of even larger numbers make for a beautiful display. You can keep harlequins with any fish as long it’s not large and predatory. It will not nip at or quarrel with any other species. Some potentially good tankmates may include cardinal tetras, one betta, neon tetras, small barbs, dwarf gouramis, danios, other small rasboras, and cory catfish.

Harlequin Rasbora Habitat and Care

Rasboras are a true freshwater family of fish and are never seen in brackish waters. They prefer the lowland waters of southeastern Asia, where the water is soft and acidic. Harlequins prefer an environment with areas of dense vegetation, an open area for swimming, a dark substrate, and subdued lighting.

An aquarium intended to house harlequin rasboras should be planted with live plants. Create open areas for swimming between stands of plants such as Cryptocoryne species, these being among the plants that inhabit the harlequin rasbora's native waters.

Harlequin Rasbora Diet and Feeding

Harlequins readily accept all foods but prefer to eat live foods whenever possible. In nature, their diet consists primarily of insects. However, they will accept frozen foods and freeze-dried foods as well as flake foods. A varied diet will ensure that digestive problems or susceptibility to disease do not occur. Brine shrimp, daphnia, and any type of worm are excellent supplemental foods, particularly when conditioning before breeding.

Gender Differences

Male harlequins are more slender than females and exhibit a rounded extension at the bottom edge of the distinctive black wedge covering the posterior of the fish. The black wedge on females is perfectly straight. The female harlequin rasbora is also larger than the male.

Breeding the Harlequin Rasbora

Harlequins are among the more difficult tropical freshwater species to breed, however, spawning may be achieved if you provide the proper conditions. Select young specimens and condition them with live foods such as daphnia and mosquito larvae before the spawning attempt. Harlequin rasbora differs from other popular rasboras in the aquarium when it comes to breeding. While other rasboras are egg-scattering spawners, harlequin rasboras are egg layers.

You can breed groups of young harlequins in a single aquarium. When spawned in groups, keep two males for every female. Hobbyists who are intent upon simulating natural conditions as closely as possible may choose to filter the aquarium water over peat, thus replicating the humic acid concentrations found in the fish's native waters, although this is not necessary if the basic water chemistry parameters (no higher than 4 dGH of hardness, pH around 6.4) are correctly maintained. Optimum water temperatures for spawning are between 76 and 80 degrees Fahrenheit. Add Cryptocorynes or similar broad-leafed plants to the breeding tank.

Once you prepare the breeding tank, introduce the breeding stock late in the day. Spawning will usually begin in the morning and is initiated by the male dancing and trembling before the female. This spawning behavior is intended to direct the female beneath a suitable plant for depositing the eggs. You may see the male nudging the sides of the female and rubbing his belly against her back to move her to the spawning location.

When ready to spawn, the female will turn upside down and rub her belly against the underside of a leaf, signaling the male to join her. The male will approach her while continuing to tremble, then wrap himself around her body and fertilize the eggs as they are released. Six to 12 eggs are laid at a time. The fertilized eggs rise and adhere to the underside of the leaves. During one to two hours, as many as 300 eggs may be laid, although 80 to 100 is more typical.

When spawning is complete, remove the breeding stock from the aquarium, as they will consume the fry once they hatch. In water temperatures of about 80 degrees Fahrenheit, the eggs will hatch in approximately 24 hours. The fry are translucent and remain attached to the leaf upon which the eggs were laid for another 12 to 24 hours, during which time the yolk sac is absorbed.

Once this process is completed, the fry become free-swimming, and at this stage, require very finely sized foods such as live infusoria for a period of seven to 14 days, after which the fry can feed upon newly hatched brine shrimp. If infusoria are unavailable, commercially prepared fry foods for an egglayer may also be used. Young harlequin rasboras then reach sexual maturity in approximately six to nine months.

More Pet Fish Species and Further Research

If harlequin rasboras appeal to you, and you are interested in some compatible fish for your aquarium, read up on:

Check out additional fish breed profiles for more information on other freshwater fish.